In piston-type internal-combustion engines the cylinder valves have been controlled until recently by a cam shaft of the engine with the intermediary of a linkage system mechanically coupling the cam shaft with the cylinder valve. As an alternative to such a valve control, in more recent engine designs electromagnetic actuators have been used for operating the cylinder valves. Such an electromagnetic actuator includes two spaced electromagnets between which an armature reciprocates in response to electromagnetic forces generated as a function of the energizing currents controlled by an electronic control system of the engine. The armature, in response to electromagnetic forces, moves against the force of resetting springs and is coupled with the respective cylinder valve to effect corresponding motions thereof. Such a system is described, for example, in U.S. Pat. No. 4,455,543.
Heretofore mechanical springs such as coil springs have been used as resetting springs, which, in principle, have been found to be satisfactory.
Operating a cylinder valve with an electromagnetic actuator controlled by an electronic control system makes possible a freely variable valve control, that is, it is feasible to vary both the opening moment and the open period of the valve as a function of the load requirements of the engine. In the design of the electromagnetic actuator, however, the oscillation characteristics of the spring/mass system composed of the armature and the cylinder valve as the mass and the mechanical resetting springs as the spring element have to be considered as a fixed, given magnitude.